Air bars or nozzles are used to direct a jet of air to impinge on the surface of a material to carry out heat and/or mass transfer functions. As is known to those skilled in the art, a plurality of air nozzles may be arranged in an array or multiple arrays to direct air impingement over a large surface of a material in web form, either on one side of the web, or both sides simultaneously. Flotation air bars are a type of air nozzle used in industrial dryers and ovens to floatingly support and convey a continuous web to be processed by thermal treatment, which may include any combination of drying, heating, curing or cooling of the web. In many cases a coating is applied to the surface of the web or a volatile material is present within the base web material which must be dried and/or heated to a particular temperature so as to facilitate thermal curing of a polymer material in the coating. Web materials commonly processed in this manner include paper, plastic film, metal foils, woven and non-woven fabrics and mats, and porous membrane materials. In many processes the volatilized materials within the web or coating after being liberated from the web surface are carried away from that surface by the spent nozzle air and conducted by an air handling system to an exhaust path, or recirculated to the air nozzles via an air handling system. Within the air handling system, the recycled air is typically re-heated by a burner or other suitable air heating means and pressurized by a fan in order to supply the heated air to the air nozzles under sufficient pressure to deliver the supply air jets at the desired impingement velocity. In some cases the materials in the recycled air either condense or are chemically altered and produce solid, semi-solid or viscous liquid forms of the liberated material. Due to the recirculation of the air within the dryer air handling system, these solid, semi-solid or viscous liquid materials can accumulate as deposits on or inside the nozzles. When deposits block the flow of air reaching or passing through the apertures of the air nozzle, the heat transfer capability of the blocked nozzles is diminished, often resulting in reduced production capacity and economic loss. Cleaning of the nozzles typically requires shut down of the process and cooling of the oven apparatus to facilitate access for manual cleaning. Clearing of the material blocking the nozzle flow usually requires some combination of brushing, scraping, loosening with compressed air blast, and vacuuming.
Although it is desirous to clean air nozzles in situ, most nozzles are designed so as to be removable from the oven enclosure to facilitate access for thorough cleaning. Removal for cleaning and remounting of the air bars is known to be an arduous and time-consuming task which increases costs of maintenance and further negatively impacts the productivity of the production line. Various tools and devices intended to clean air nozzles in-situ such as scraper knives or brushes fastened to extension poles have been fashioned by maintenance personnel with limited cleaning effectiveness. In some cases, such devices have been known to damage the integrity of the nozzles by deforming the nozzle apertures, resulting in adverse effects in product quality such as drying defects, marking, or web breaks.
A particular family of processes wherein curable silicone coatings are applied to a web, such as in the production of release liners for pressure sensitive adhesive tapes, films and sheets, suffers from extensive generation of dust buildup within the nozzles and air handling systems of the drying and curing ovens used for this purpose. Many of these silicone release liner products are dried and cured in flotation ovens. In this type of oven, not only is heat transfer and drying capacity diminished when deposits block nozzle apertures, the conveyance function of the flotation dryer is also compromised, leading to web product defects. Known apparatus and methods used to attempt cleaning of flotation nozzles in situ are only minimally effective. Deposits inside of the air bar apertures and flow distribution elements within the body of the air bar cannot be reached effectively by most mechanical means when accessing the air bars in situ. Further, cleaning of the flotation air bars by improper mechanical methods can result in degradation and even permanent damage to the apertures adversely affecting the stable flotation conveyance of the web as well as adverse heat transfer and drying effects.
In most cases, thorough cleaning of air bars can be practically accomplished only by removal from the oven and careful washing and/or vacuuming steps requiring a significant amount of downtime.
It is therefore an aspect of embodiments disclosed herein to provide an apparatus (tool) which can effectively remove buildup within the flotation air nozzle while in situ. It is a further aspect of embodiments disclosed herein to ensure that the mechanical interaction of the cleaning tool with the air bars is not detrimental to the mechanical integrity of the nozzle apertures. Further, in certain embodiments, the sequence of cleaning steps provides for removal of dust/material from the nozzles so as to prevent re-accumulation of dust from deposits already freed from the internal surfaces of the air bars, thus extending the time between cleanings.